JP2002251079A - Image forming apparatus and rotating body speed detecting apparatus - Google Patents

Abstract

(57) [Problem] To easily and accurately detect a moving speed of an endless belt which fluctuates due to thermal expansion. SOLUTION: An electrostatic transport belt 9a for transporting a transfer material S for forming an image, a driving roller 9b for driving the belt 9a, a driven roller 9c driven by the belt 9a,
9e, an image forming unit for forming an image on the belt 9a or the transfer material S conveyed to the belt 9a, a sensor 20 for detecting a moving speed of the belt 9a, and a detection result of the sensor 20. Speed control means 21 for controlling the moving speed of the belt 9a based on the rotation of the belt 9a. The sensor 20 detects the speed of the driven roller 9c (or the driven roller 9e) driven by the electrostatic transport belt 9a once every one rotation.
The moving speed of the electrostatic transport belt 9a is detected by generating a pulse signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, and an electroless system which include an endless belt for carrying an image or conveying a medium on which an image is formed, and for forming an image by an electrophotographic system.
The present invention relates to an image forming apparatus such as a facsimile and a speed detector for a rotating body.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic method or an electrostatic recording method for an image forming process, a cylindrical photosensitive drum is used as an image carrier, and a photosensitive drum around the photosensitive drum is used. There are well-known types in which a charger, an exposure unit, a peripheral device such as a developing unit and a cleaning unit, and a transfer material transport mechanism (transfer material transport unit) are provided.

In recent years, in order to further improve the functions of a photosensitive drum, a transfer material transport mechanism, and the like, an endless belt using a photosensitive member serving as an image carrier instead of the photosensitive drum has been adopted. An image forming apparatus using an endless belt as a transfer material conveying mechanism has been developed.

As described above, in an image forming apparatus employing an endless belt for a photosensitive member or a transfer material transport mechanism, many functions can be improved, but disadvantages inherent to the belt mechanism are encountered. A speed control means for controlling a change in the moving speed of the endless belt due to a rise in the temperature of the inside of the image forming apparatus or a change in the use environment temperature is indispensable.

[0005] Usually, the moving speed of the endless belt must match the recording position with high accuracy, so that the outer diameter tolerance of the driving roller for driving the endless belt is set strictly. However, the drive roller expands and contracts due to a rise in the temperature of the inside of the image forming apparatus main body and a change in the use environment temperature, and the moving speed of the endless belt changes, the recording position accuracy deteriorates, and image quality deteriorates. A problem arises.

Therefore, conventionally, as a speed control means for controlling the moving speed of the endless belt, the drive roller is made of a material which is unlikely to thermally expand, the temperature near the drive roller is measured, and the diameter of the drive roller is predicted. Such methods have been adopted.

[0007]

However, the above-described measures may not be able to completely prevent color shift and density unevenness due to slight positional shift.

[0008] Japanese Patent Application Laid-Open No. 4-172376 and
In JP-A-234064 and JP-A-11-231754, in order to control the speed fluctuation due to the eccentricity of the driving roller, a rotary encoder for detecting the rotational angular velocity is provided on the shaft of the driven roller driven by an endless belt, An apparatus that controls the rotation speed of a motor that rotates a driving roller using the detection result is disclosed.

Such a method of detecting the moving speed of the endless belt from the driven roller is effective not only for controlling the speed fluctuation due to the eccentricity of the driving roller but also for controlling the speed fluctuation itself due to the thermal expansion.

However, there is a problem that using a precise rotary encoder leads to a considerable increase in cost.

An object of the present invention is to detect the moving speed of an endless belt, which fluctuates due to thermal expansion, more simply and accurately.

[0012]

A typical configuration of the present invention for achieving the above object is an endless belt for carrying an image or conveying a medium on which an image is formed, and a driving roller for driving the endless belt. And a driven roller driven by the endless belt, image forming means for forming an image on the endless belt or a medium conveyed by the endless belt, speed detecting means for detecting a moving speed of the endless belt, Speed control means for controlling the moving speed of the endless belt based on the detection result of the speed detection means, wherein the speed detection means outputs one pulse each time a driven roller driven by the endless belt makes one rotation. The moving speed of the endless belt is detected by generating the following signal.

With the above configuration, the mechanical accuracy of the pulse signal generator, for example, the eccentricity of the roller can be ignored, and the moving speed of the endless belt can be detected more simply and accurately.

Further, the speed detecting means can easily output the signal by generating the signal by a notch or a hole provided in a part of the driven roller.

In addition, a notch or a hole is provided at the shaft end of the driven roller, and the speed detecting means is positioned on a bearing of the driven roller or a bearing holding member for holding the bearing. By generating a signal by passing and blocking light by a notch or a hole provided at the shaft end of the driven roller, the rotation of the driven roller is stably detected. The position is determined, and the signal can always be generated stably.

[0016] The speed control means may determine the eccentricity of the driving roller by using the pulse number of the driven roller as a reference when the peripheral length of the driven roller and the peripheral length of the driving roller are substantially common multiples. An error due to the generated speed fluctuation can be eliminated, and the accuracy of the speed control of the endless belt can be further improved.

[0017] The speed control means may use the number of pulses of the driven roller as a reference when the peripheral length of the driven roller and the peripheral length of the endless belt are substantially multiples, so that the thickness unevenness of the endless belt is obtained. An error due to speed fluctuations caused by the above-mentioned factors can be eliminated, and the accuracy of the speed control of the endless belt can be further improved.

Further, when a plurality of the image forming means are provided at a predetermined pitch on the endless belt,
By configuring the linear expansion coefficient of the driven roller and the linear expansion coefficient of the member that determines the pitch of the image forming unit to be substantially the same, the driven roller thermally expands and is slower than the actual moving speed of the endless belt. What was detected,
What is expanded by the thermal expansion at the installation position of the image forming means is substantially balanced, and the deviation of each color when an image is actually formed is eliminated.

Also, in a rotating body speed detecting device for detecting a speed of the rotating body, the rotating body has a sensor for generating a signal by passing and blocking light, and a part of the shape of the rotating body is provided. By providing a notch or a hole and generating a signal in the sensor by the notch or the hole, the speed of the rotating object can be easily detected.

Further, since the sensor is directly positioned on the bearing of the rotating body or the bearing holding member for holding the bearing, the sensor can be accurately installed and a signal can be accurately detected.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings. However,
The dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions, and in particular, Unless otherwise described, the scope of the present invention is not intended to be limited to them.

[First Embodiment] FIG. 1 is a sectional view schematically showing a color image forming apparatus according to an embodiment of the present invention.

The color image forming apparatus shown in FIG. 1 is provided with four photosensitive drums 1 (1a, 1b, 1c, 1d). A charging means 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1, and an exposure means 3 for irradiating a laser beam based on image information to form an electrostatic latent image on the photosensitive drum 1. (3a, 3b, 3c, 3
d) developing means 4 (4a, 4b, 4c, 4d) for adhering toner to the electrostatic latent image to visualize it as a toner image, and transfer means 5 for transferring the toner image on photosensitive drum 1 to a transfer material (5a, 5b, 5c, 5d), cleaning means 6 (6a, 6b, 6c, 6d) for removing the post-transfer toner remaining on the surface of the photoreceptor drum 1 after the transfer, and the like, constitute the image forming means. Have been.

Here, the photosensitive drum 1 as an image carrier
Charging means 2 as a process means acting on this,
The developing means 4 and the cleaning means 6 for removing toner are integrally formed as a cartridge, and the process cartridge 7
(7a, 7b, 7c, 7d).

The transfer material S fed from the feeding section 8 is conveyed to the image forming means by conveying means 9 constituted by an electrostatic conveying belt, and the color toner images are sequentially transferred to record the color images. Then, the image is fixed by the fixing unit 10 and discharged to the discharge unit 13 by the discharge roller pairs 11 and 12.

In the case of double-sided recording, before the transfer material S is fixed in the fixing unit 10 and discharged by the discharge roller pairs 11 and 12, the discharge roller pairs 11 and 12 are rotated in reverse, so that the double-sided conveyance path 15 is formed. (Arrow A direction). The transfer material S conveyed to the two-sided conveyance path 15 passes through a skew feeding roller 16 in front of the apparatus main body, is conveyed vertically downward to a U-turn roller 17, and is formed by the U-turn roller 17 and the registration roller 8d. Transported to

Next, the configuration of each part will be described sequentially.

(Feeding Unit) The feeding unit 8 includes a sheet feeding cassette 8
a, a multi-feeding tray 8b as a multi-feeding device, a multi-feeding unit 8c, and registration rollers 8d.

The paper feed cassette 8a stores a plurality of transfer materials S and is loaded at the bottom inside the apparatus main body. Paper cassette 8a
When forming an image from the cassette pickup roller 8
The transfer material S is separated and conveyed one by one by a1, and is conveyed to the image forming unit by the cassette conveyance roller 8a2 and the registration roller 8d.

Next, the multi-sheet feeding tray 8b is normally stored in the front of the apparatus main body, but when used, the multi-sheet feeding tray 8b is rotated and opened from the apparatus main body to set a plurality of transfer materials S. I do. When forming an image from the multi-sheet feed tray 8b, the transfer material S is separated and conveyed one by one by the multi-pickup roller 8c1.
The sheet is conveyed to the image forming unit by the registration roller 8d.

At this time, the paper feeding path from the multi-feeding device which uses a transfer material such as a thick paper, an envelope, and special paper which is relatively unlikely to be electrostatically attracted to the belt surface or has a high stiffness is used for the transfer. When the material arrives at the surface of the belt, the transfer material is formed of only R so that the leading and trailing ends of the transfer material are along the belt surface and have a curve such that the central portion floats.
As shown in FIG. 1, the paper feed path from the cassette has a curve that warps against the surface of the electrostatic transport belt, but the transfer material fed from the cassette is relatively weak.
It has been found that there is no problem even if a cassette paper feeding path as shown in FIG. 1 is used in order to use a transfer material which is easily electrostatically attracted to the belt surface.

The separation and conveyance of the transfer material in the sheet feeding cassette 8a and the multi-feeding section 8c are performed by a sheet feeding motor (not shown) in the feeding section via a gear drive train.

(Image Forming Structure) The photosensitive drum 1 as an image carrier is formed by applying an organic photoconductive layer (OPC) to an outer peripheral surface of an aluminum cylinder. The photosensitive drum 1 is rotatably supported at both ends by flanges, and is driven to rotate in the counterclockwise arrow direction by transmitting a driving force from a drive motor (not shown) to one end.

Each charging means 2 is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photosensitive drum 1 and a charging bias voltage is applied by a power supply (not shown) to thereby charge the photosensitive drum. This is for uniformly charging the surface of the drum 1.

The exposing means 3 has a polygon mirror, and the polygon mirror is irradiated with image light corresponding to an image signal from a laser diode (not shown).

The developing means 4 is adjacent to the toner storage sections 4a1, 4b1, 4c1, 4d1 storing toners of the respective colors of black, cyan, magenta, and yellow, and is rotatably driven by a drive section (not shown). In addition, a developing roller 4a2 that performs development by applying a developing bias voltage from a developing bias power supply (not shown)
4b2, 4c2, 4d2, etc.

In the inside of an electrostatic transport belt 9a to be described later, transfer means 5a, 5 opposed to the four photosensitive drums 1a, 1b, 1c, 1d and in contact with the electrostatic transport belt 9a.
b, 5c, and 5d are respectively provided. These transfer means 5 are connected by a transfer bias power supply (not shown), and a positive charge is transferred from the transfer means 5 to the transfer conveyance belt 9a.
Is applied to the transfer material via the photoconductor drum 1, and the negative color toner images on the photoconductor drum 1 are sequentially transferred to the transfer material being in contact with the photoconductor drum 1 to form a color image.

(Transfer Material Conveying Structure) The transfer material S is conveyed from the feeding section 8 to the image forming area by the conveying means 9.

An electrostatic transport belt 9a as an endless endless belt (transfer material carrier) constituting the transport means 9
Is stretched and supported by four rollers of a driving roller 9b, a tension roller 9d, and driven rollers 9c, 9e, and is disposed to face all the photosensitive drums 1a, 1b, 1c, 1d. The driving roller 9b needs to be driven stably without slipping on the electrostatic transport belt 9a. Therefore, in consideration of the driving grip performance and durability of the electrostatic transport belt 9a, a thin metal roller having a thickness of about 1 mm is used. It is made of rubber or the like.

However, since the elastic member such as rubber has a larger linear expansion coefficient than a metal material, the elastic member expands or contracts due to a temperature change due to a rise in temperature inside the apparatus or a change in the use environment, and the diameter of the drive roller 9b is reduced. Will change. for that reason,
Even if the driving roller 9b drives the electrostatic transport belt 9a at the same number of revolutions, the belt driving speed (moving speed of the belt 9a) is changed, and the recording position accuracy is deteriorated, and phenomena such as deterioration of image quality occur. I will.

Therefore, it is necessary to control the speed (moving speed) of the electrostatic transport belt 9a.
As shown in FIG. 5, a sensor 20 as a speed detecting means
Generates a one-pulse signal each time the driven roller 9c (or the driven roller 9e) that is driven and rotated by the electrostatic transport belt 9a makes one rotation, thereby detecting the speed of the electrostatic transport belt 9a. The speed control means 21 is driven based on the driving motor 22 which is the driving source of the driving roller 9b.
The moving speed of the electrostatic transport belt 9a is controlled by controlling the number of rotations of the drive motor 22.

In the method of detecting one pulse each time the driven roller makes one rotation, the rotation speed becomes uneven due to the eccentricity of the detected roller itself, but the time for one rotation does not always change, so that an error occurs on the detection side. There is a merit that there is not.

As a method of generating one pulse signal each time the driven roller makes one rotation, for example, there is a method in which a part of the shape of the driven roller is formed as a notch or a hole. In particular,
As shown in FIGS. 2 and 3, there is a type in which the end of the shaft 25 of the driven roller 9c (or the driven roller 9e) is D-cut (or a groove or the like) (D-cut portion 26 in the drawings). However, if the signal cut is started immediately after the signal generating section by simply using the D cut, it takes approximately one rotation to start signal picking. Therefore, when it is necessary to reduce the time, a method of making D-cuts on both sides of the shaft tip (see FIG. 4 (a)) is required.
By using a pulse signal (see Fig. 4 (b))
A signal is generated not for one pulse but for one rotation of the driven roller, and several pulses are generated.
By taking a pulse for each rotation, it is also possible to reduce the waiting time before starting to take a signal.

In order to further increase the accuracy in controlling the speed of the electrostatic transport belt 9a, as shown in FIG. 5, when the peripheral length of the driven roller and the peripheral length of the driving roller are substantially common multiples, as shown in FIG. By using the number of pulses of the driven roller as a reference, it is possible to eliminate a detection error caused by speed unevenness due to eccentricity of the driving roller and the like. The circumference of the driven roller and the circumference of the electrostatic transport belt 9a are substantially common multiples. There is a method in which a detection error caused by uneven speed due to uneven thickness of the electrostatic transport belt 9a can be eliminated by using the number of pulses of the driven roller as a reference.

However, to further reduce the detection error,
The actual thermal expansion of the drive roller diameter is about 0.34 at 30 ° C.
%, The thermal expansion of the driven roller diameter for controlling the speed is about 0.035% at a temperature rise of 30 ° C., and the coefficient of thermal expansion of the driven roller is quite small, but this thermal expansion becomes a measurement error as it is and is ignored. Can not do it.

Therefore, as shown in FIG. 6, a member (FIG. 6) for determining the linear expansion coefficient of the driven roller and the pitch of the photosensitive drums 1 of the respective image forming means arranged at a predetermined pitch on the electrostatic transport belt 9a. By making the coefficient of linear expansion of the middle side plate 27) substantially the same, the time period for one rotation of the driven roller becomes longer, so that it is erroneously determined that the driven roller is moving at a speed lower than the actual belt speed. Detect
After all, moving the belt at a faster speed than the target,
There is a method in which the installation distances of the image forming units of the respective colors are extended by thermal expansion, and the distances are substantially balanced, and there is no deviation of the respective colors when an image is actually formed.

Further, in order to stably detect the speed of a driven roller as a rotating body, the positions of the roller and the sensor become considerably important. This is necessary in order to always generate a signal stably, and as shown in FIG. 7, a bearing holding member 24 (or a bearing) that holds the bearing 23 of the driven roller 9c (or the driven roller 9e), as shown in FIG. 23) there is one in which the sensor 20 is directly positioned. With this configuration, the position of the sensor 20 and the driven roller 9c whose shaft end is D-cut as described above can be accurately positioned, and the speed of the driven roller 9c can always be detected stably. Based on this detection result, the electrostatic transport belt 9a can be rotationally driven at a stable moving speed.

With the above-described structure, the electrostatic transport belt 9a is driven stably, and the transfer material S is electrostatically attracted to the outer peripheral surface facing the photosensitive drum 1 so that the transfer material S is transferred to the photosensitive drum 1. Are circulated by the drive roller 9b so as to make contact. As a result, the transfer material is transferred to the electrostatic transport belt 9a.
And the toner image on the photosensitive drum 1 is transferred.

At the most upstream position of the electrostatic transport belt 9a, there is provided a suction roller 9f for holding the transfer material together with the belt 9a and for attracting the transfer material to the electrostatic transport belt 9a. When the transfer material is conveyed, a voltage is applied to the attraction roller 9f to form an electric field between the transfer roller and the grounded roller 9c facing the transfer roller 9f.
A dielectric polarization is generated between a and the transfer material to generate an electrostatic attraction force therebetween.

(Auxiliary Conveying Structure) The Electrostatic Conveying Belt 9a
When the transfer material S is transported by using the auxiliary member, the transfer material S is configured not to be separated from the electrostatic transport belt 9a by the auxiliary member. As described later, the electrostatic transport belt 9a
It also functions as a moving unit for moving the to the second position.

More specifically, a plurality of transport auxiliary rollers 14 are provided as auxiliary members rotatable and rotatable on the front side of the electrostatic transport belt 9a, and the transport auxiliary rollers 14 are driven by a cam mechanism (not shown). It is configured to be able to move integrally in the left-right direction.

When performing color recording, the transport assist roller 14 is retracted to the left to transfer the transfer transport belt 9a.
Away from On the other hand, when performing monochrome recording, the cam mechanism operates to move the transport assist roller 14 to the right, abut on the electrostatic transport belt 9a, and push the belt 9a. Thereby, the electrostatic transport belt 9a
Is kept in contact with the black photosensitive drum 1d, but is separated from the other photosensitive drums 1a, 1b, 1c.

(Fixing Unit) The fixing unit 10 fixes the image (toner image) formed on the transfer material by applying heat and pressure.

Reference numeral 10a denotes a cylindrical fixing belt having an electromagnetic induction heating layer, which is guided by a belt guide member 10c having a built-in magnetic field generating means including an exciting coil and a T-shaped magnetic core.

Reference numeral 10b denotes an elastic pressure roller which forms a fixing nip portion N having a predetermined width with a predetermined pressing force with the belt guide member 10c with the fixing belt 10a interposed therebetween.

The pressure roller 10b is driven to rotate by driving means (not shown), and the cylindrical fixing belt 10
a rotates and the fixing belt 10a generates electromagnetically induced heat by power supply from an excitation circuit (not shown) to the excitation coil.

In a state where the temperature of the fixing nip N has risen to a predetermined temperature and the temperature has been controlled, the transfer material S on which the unfixed toner image conveyed from the image forming unit is formed is applied to the fixing belt 10a of the fixing nip N by the fixing belt 10a. The image surface is introduced between the pressure roller 10b and the fixing belt 10a, and the image surface is brought into close contact with the outer surface of the fixing belt 10a at the fixing nip portion N, and is fixed together with the fixing belt 10a. Are conveyed.

In the process in which the transfer material is nipped and conveyed in the fixing nip portion N together with the fixing belt 10a, the fixing belt 10a is heated by electromagnetic induction heat and the unfixed toner image on the transfer material S is heated and fixed. .

[Other Embodiments] In the above embodiment,
Although an image forming apparatus in which four single-color image forming units are arranged is illustrated, the number of use is not limited.
What is necessary is just to set suitably as needed.

In the above-described embodiment, a printer is exemplified as an image forming apparatus. However, the present invention is not limited to this. For example, other image forming apparatuses such as a copying machine and a facsimile apparatus and an endless belt may be used. The image formed on each photosensitive drum is primarily transferred onto the intermediate transfer belt by using the intermediate transfer belt (intermediate transfer body), and the intermediate transfer belt carries the intermediate transfer belt to the transfer medium such as a recording sheet. An image forming apparatus that collectively transfers (secondary transfer) the toner images of each color carried on the transfer belt may be used.
The same effect can be obtained by applying the present invention to the image forming apparatus.

[0061]

As described above, according to the present invention,
It is possible to accurately detect a change in the speed of the endless belt due to a rise in the temperature of the inside of the image forming apparatus or a change in the use environment temperature, and it is possible to suppress a fluctuation in the speed of the endless belt. Density unevenness can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a color image forming apparatus configured by controlling a belt speed of a belt conveying device according to the present invention.

FIG. 2 is a schematic diagram of a one-revolution one-pulse signal generator of a driven roller according to the present invention.

FIG. 3 is a simplified diagram showing FIG. 2 in a more simplified manner.

FIG. 4 shows an example of a configuration for generating a two-pulse signal by one rotation of a driven roller unit according to the present invention (FIG. 4 (a) shows both-side D-cut, FIG. 4 (b) shows two-pulse generation from one D-cut) Figure showing

FIG. 5 is a diagram illustrating speed fluctuations of a driving roller, a driven roller, and an endless belt of the image forming apparatus according to the present invention.

FIG. 6 shows a photosensitive drum 1 of each image forming unit according to the present invention.
Schematic showing the configuration of the member that determines the pitch of the roller and the driven roller

FIG. 7 is an explanatory view showing the vicinity of a sensor attachment portion for speed detection according to the present invention.

[Explanation of symbols]

N: Fixing nip S: Transfer material 1: Photoconductor drum 2: Charging means 3: Exposure means 4: Developing means 4a1, 4b1, 4c1, 4d1: Toner storage unit 4a2, 4b2, 4c2, 4d2: Developing roller 5: Transfer Means 6 Cleaning means 7 Process cartridge 8 Feeding section 8a Feeding cassette 8a1 Cassette pickup roller 8a2 Cassette transport roller 8b Multi feed tray 8c Multi feed section 8c1 Multi pickup roller 8c2 Multi transport Roller 8d: Registration roller 9: Transport means 9a: Electrostatic transport belt 9b: Drive rollers 9c, 9e: Followed roller 9d: Tension roller 9f: Adsorption roller 10: Fixing unit 10a: Fixing belt 10b: Pressure roller 10c: Belt guide Members 11, 12 ... discharge rollers Pair 13: Discharge unit 14: Conveyance auxiliary roller 15: Double-sided conveyance path 16: Oblique feeding roller 17: U-turn roller 20: Sensor 21: Speed control means 22: Drive motor 23: Bearing 24: Bearing holding member 25: Shaft 26: D-cut portion 27 ... side plate (member for determining the pitch of the photosensitive drum of each image forming means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ichiyasu Miyamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Seiji Obata 3- 30-2 Shimomaruko, Ota-ku, Tokyo F term (reference) in Canon Inc. PB39

Claims (8)

[Claims] 1. An endless belt that carries an image or conveys a medium on which an image is formed, a driving roller that drives the endless belt, a driven roller that follows the endless belt, and the endless belt or the endless belt. Image forming means for forming an image on a conveyed medium; speed detecting means for detecting a moving speed of the endless belt; controlling a moving speed of the endless belt based on a result detected by the speed detecting means. Speed control means, wherein the speed detection means detects a moving speed of the endless belt by generating a signal of one pulse every time a driven roller driven by the endless belt makes one rotation. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the speed detecting unit generates a signal by a notch or a hole provided in a part of the driven roller. 3. A notch or a hole is provided at a shaft end of the driven roller, and the speed detecting means is positioned on a bearing of the driven roller or a bearing holding member for holding the bearing. 2. The image forming apparatus according to claim 1, wherein a moving speed of the endless belt is detected by generating a signal by transmitting and blocking light by a notch or a hole provided at a shaft end of the driven roller. 3. 4. The speed control means according to claim 1, wherein said peripheral length of said driven roller and said peripheral length of said drive roller are substantially common multiples.
The image forming apparatus according to claim 1, wherein the number of pulses of the driven roller is used as a reference. 5. The apparatus according to claim 1, wherein the speed control means uses a pulse number of the driven roller as a reference when a peripheral length of the driven roller and a peripheral length of the endless belt are substantially common multiples. An image forming apparatus according to claim 1. 6. When a plurality of image forming means are provided on the endless belt at a predetermined pitch, a linear expansion coefficient of the driven roller and a linear expansion coefficient of a member for determining a pitch of the image forming means are different. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to be substantially the same. 7. A rotator speed detecting device that has a rotator and a sensor that generates a signal by passing and blocking light, and detects a speed of the rotator. A rotating body speed detecting device, wherein a notch or a hole is provided, and a signal is generated by the sensor by the notch or the hole, thereby detecting a speed of the rotating body. 8. The rotating body speed detecting device according to claim 7, wherein the sensor is directly positioned on a bearing of the rotating body or a bearing holding member that holds the bearing.